It is known that one of the major problems encountered in practical application, particularly for use in washing machines, is to introduce measured quantities of a liquid into another body of liquid. In order to add a liquid chemical solution to another body of liquid, the U.S. Pat. Nos. 3,095,121 and 4,306,581 employ suction means connected to the circulation hose of the liquid body which is to receive the said chemical product. The U.S. Pat. No. 4,218,264 shows a dishwasher in which the suction created by the pump controlling the water circulation during the wash and rinse cycle, draws out from dispensers the liquid detergent to be mixed with the water.
These examples of known technology all have the disadvantage of needing water, or another liquid in motion to draw out from the dispenser the necessary quantities of the liquid additive or detergent. This causes a complexity in the necessary equipment and constitutes a difficulty in controlling the exact dosage of the liquid substance to be added.
To eliminate the drawbacks inherent with pumps that are not automatic, peristaltic pumps have also been used; nevertheless these are associated with high installation and maintenance costs.
In any event, the introduction of the additive liquid by means of circulation pumps which are already in the washing machines, as aforesaid, has the drawback of not permitting an exact and efficient dosage of the additive; while other pumps are not automatic or are relatively complex to operate and are also expensive.
These are great drawbacks when we consider that washing machines, whether they be industrial or domestic, should be highly reliable and cost-effective.